TPI July 2014

Corrosion prevention fluids: Corrosion preventives have more stringent requirements and better-defined test methods than metal processing fluids. Some of the more common tests involve cabinets that control the temperature and humidity. In addition, the handling of coated test panels must be controlled relative to the amount of corrosion preventive that is applied to the surface. Most testing is conducted with duplicate or triplicate panels. The water source must be pure to eliminate any contaminants (chlorides or sulphates) that could affect the results. • The Joint Army-Navy (JAN) cabinet test, in use since the 1940s, uses a temperature maintained at 120°F with 100 per cent relative humidity. It is a condensing environment, meaning that water collects on the surface of the test panel and runs down the panel and the coating. • The salt spray cabinet test (ASTM B117) exposes specimens to a 5 per cent salt spray in the form of a fog; the temperature is maintained at 100°F. • The GM 10-cycle test, developed by General Motors to evaluate corrosion preventives, has been adopted by many suppliers aligned with GM. This method is similar to the JAN but it runs at 100°F in a non-condensing environment. In addition, it runs ten cycles, each cycle consisting of 18 hours in the cabinet and six hours out of the cabinet. Troubleshooting When you first investigate a rust issue, it is important to learn the metal surface’s exposure history; you need to trace back through all of the processes to determine where the corrosion began. The investigation should involve every process and fluid that contacts the parts. Only by tracing the entire process do you have a chance at determining the application that has the greatest impact on the corrosion problem. The fluids involved in the process should be evaluated for fitness for use relative to fresh fluid. Cause-and-effect diagrams can help you find the root cause. Corrosion – at what cost? According to ‘Corrosion Costs and Preventive Strategies in the United States’, a 2002 study commissioned by the Federal Highway Administration, undertaken by CC Technologies Laboratories Inc, and sponsored by NACE International, the direct costs of metal corrosion in the US total $276bn annually. To put this into perspective, it amounted to more than 3 per cent of US gross domestic product. Corrosioncomeswithanother cost.Amanufacturedcomponent or assembly that fails or requires a remedial corrosion prevention treatment results in customer dissatisfaction. Using comprehensive corrosion control methods is critical in minimising both types of costs.

need just a few hours of protection until parts go to the next process, while others store the parts for weeks until they are needed. The storage and coolant conditions are critical factors in determining how long the fluids provide corrosion protection. The factors that affect the duration of corrosion protection include upstream manufacturing processes; surface cleanli- ness; the corrosion preventive’s condition during application; the quality of the application method; the packaging used to enclose the part; and the storage environment. Knowing about upstream manufacturing processes and fluids used in those processes is a help in understanding how to handle the second factor, surface cleanliness. What sorts of metalworking fluids have been used on the part? Has the part been stored between manufacturing steps? How has it been handled? If the part has metalworking fluid residues, if it has been stored in an area with fines and dust, or if it has been handled manually by workers without gloves, surface cleanliness is an issue that must be addressed. Second, the fluid delivery system must have adequate capacity to wet the parts thoroughly and must be maintained to deliver a consistent quantity of corrosion preventive to the parts. A good filtration system – one that minimises the sizes and quantities of fines, minimising the levels of tramp oils, chlorides and sulphates – extends the fluid’s ability to prevent corrosion. Also, the fluid’s concentration must be at the correct level; it should be measured with an instrument more precise than a refractometer. Third, after coating but before packaging, good handling practices are necessary to maintain the protective film’s integrity. Gloves are necessary to prevent the oils in workers’ skin from coming into contact with the steel. Fourth, the packaging to enclose the parts must be of sufficient quality and in good condition, not torn or damaged, to prevent direct access to the coated parts. Finally, the storage environment must be controlled to prevent gross fluctuations of temperature and humidity (less than 15°F and less than 10 per cent change in relative humidity in a 24-hour period). Measuring a corrosion preventive’s effectiveness A number of short-term and long-term tests can measure corrosion protection. All of these tests are designed to mimic real-life applications under accelerated conditions. You should be aware that the interpretation of the test results can be just as important as setting up and controlling the conditions of the tests. Metal removal fluids: For metal removal fluids, a couple of tests assess the interaction of the fluid and metal chips that are generated. Most chip tests involve a fixed amount of chips covered by a measured amount of coolant. The wet chips are then set on filter paper or metal blocks to determine the rust potential. Most tests last a few hours.

Quaker Chemical Corp – USA www.quakerchem.com

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July 2014 Tube Products International